1. Field of the Invention
The present invention relates to a wind turbine and, in particular, to a gearbox interposed between a rotor of a wind turbine and an electrical generator.
2. Background Art
It is known to use a planetary gearbox to drive an electric generator in response to rotation of a rotor of a wind turbine. The rotor provides a low speed, high torque input to the gearbox. The gearbox provides a high speed, low torque output to the generator. This type of gearbox has been used in this application for approximately twenty years. It is also known that the planet gears of such a gear box, and the bearings associated therewith, are subjected to high lateral loads and thus suffer from high rates of wear under such demanding usage and do not provide ready accessibility for the maintenance, repair and replacement of these key wear components.
U.S. Pat. No. 6,420,808 titled “Gearing for Wind Generator” shows a gearbox for driving a generator by wind force. The gearbox includes a multi-stage epicyclic gearing arrangement and a spur gear stage for the drive output to the generator. The input from the turbine rotor drives a ring gear to rotate about an axis. The ring gear meshes with planet gears at the interior of the ring gear, and the planet gears are fixed in position in a housing. The planet gears drive a sun gear rotatable about the centerline of the gear box and this in turn, through a set of spur gears, drives an output shaft connected to the generator. This gear box suffers from several limitations that reduce its reliability of operation, and make repair and replacement of key wear components more difficult. Planet gears 19 carried by planet gear shafts 17 overhang the adjacent outer bearings for these shafts (i.e., are mounted cantilevered relative to these bearings). This arrangement generates increased lateral forces on the outer and inner bearings. Moreover, the inner bearing is narrower and of smaller inner and outer diameter than the outer bearing, thereby reducing its load carrying capacity relative to the outer bearing. The reduced inner and outer diameters are necessitated by space constraints imposed by the inner end of the ring carrier 12. In addition, access to both the inner and outer bearings for servicing requires disassembly of the entire gear box.
As shown in U.S. Pat. No. 6,148,940, commonly assigned to General Electric Company, it is also known to use planetary gearboxes for motorized wheels of a large off-road vehicle, specifically, a vehicle used in open-pit mining. An electric motor, having a high speed, low torque output, is connected with the input of the gearbox. The gearbox in response provides a low speed, high torque output to the wheel, to rotate the wheel.
U.S. Pat. No. 5,663,600 shows a large planetary gear set that is used in transferring torque from a wind rotor to a shaft/generator. The gear set includes a ring gear that rotates with the rotor.